Manufacture of lignite binder pitch

ABSTRACT

Binder pitch suitable for metallurgical electrode production is prepared from crude pitch obtained from the low-temperature carbonization of lignite. Aliphatic hydrocarbons contained in the crude pitch are removed by solvent extraction prior to thermal treatment such as delayed coking or thermal cracking. Binder pitch product is recovered as a residual fraction of the oil produced in the thermal treatment.

United States Patent [191 Berber et al.

. 11] 3,801,342 [451 Apr. 2, 1974 MANUFACTURE OF LIGNITE BINDER PITCH [75] Inventors: John S. Berber; Richard L. Rice,

both of Morgantown, W. Va.

[22] Filed: Nov. 16, 1970 [21] Appl. No.: 89,671

[52] US. Cl 106/284, 106/273, 208/22, 208/44 [51] Int. Cl. C08h 13/00, C08h 17/08, ClOc 3/00 [58] Field of Search 106/38.8, 273, 284; 208/22, 45; 264/29, 105

[56] References Cited UNITED STATES PATENTS 2,683,107 7/1954 Juel .Q. 106/284 X 2,955,079 10/1960 Foley 208/22 FOREIGN PATENTS OR APPLICATIONS 823,381 11/1959 Great Britain 106/284 828,116 2/1960 Great Britain 106/284 OTHER PUBLICATIONS Abraham, Asphalts and Alied Substances, 6th Ed., Vol. two, N.Y. D. Van Nostrand Co. Inc., TN 853, A35 1960 C4. pages 39-5l relied on.

Primary Examiner-Harry Wong, Jr. Attorney, Agent, or FirmRoland I-I. Shubert [5 7 ABSTRACT Binder pitch product is recovered as a residual fraction of the oil produced in the thermal treatment.

6 Claims, 1 Drawing Figure mm mrs 2:914 3,801,342

I LOW-TEMPERATURE LIGNITE PITCH 3 2 EXTRACTION 4- -SOLVENT 5 I 4 7\ DISTILLATION 6 WASHING ALIPHATICS /4 THERMAL I DELAYED CRACKING COKING 3 l6 OIL OIL l9 DISTILLATION -LPDISTILLATE 20% BINDER //vv/vr0/?s JOHN S. BERBER RICHARD L. RICE Ema Qua;

A TTOR/VEYS BACKGROUND OF THE INVENTION Low temperature carbonization of lignite produces tar and a char residue. The char finds use as power plant fuel, for synthesis gas production and for blending with other coals to produce metallurgical coke. Low temperature tar can be utilized as a source material for organic chemicals and binder pitches for use in making carbon electrodes.

Pitch comprises the residue from crude tar distillation. It typically has a boiling point above about 350C and is an amorphous solid material at room temperature. Lignite pitch differs from pitch derived from bituminous coal tars in that it generally has a lower percentage of fixed carbon and a lower carbon/hydrogen atomic ratio.

We have previously found that lignite pitch can be upgraded by either delayed coking techniques or by thermal cracking to produce a number of useful products. When the pitch is-thermally cracked, products include coke, oil and a gas rich in ethylene. Distillation of the oil fraction leaves a pitch residue having desirable characteristics for use as a binder material. Electrodes prepared from this binder pitch and lignite coke showed somewhat higher carbon consumption, higher resistivity and lower physical strength than did standard electrodes when used in alumina reduction.

SUMMARY OF THE INVENTION We have now found that solvent extraction of the aliphatic hydrocarbons contained in low temperature lignite pitch substantially improves the quality of binder pitch recovered-as a product of delayed coking or thermal cracking. Preferred solvents include saturated, aliphatic hydrocarbons having about 7 to 9 carbon atoms.

DETAILED DESCRIPTION OF THE INVENTION Our invention will best be understood and appreciated from the following description of the process taken in connection with the accompanying drawing in which: 7

The FIGURE is a diagrammatic flow sheet of our process.

Referring now to the drawing, a low temperature lignite pitch material 1, preferably in the form of pulverized particles, isfed either intermittently or continuously into extraction zone 2.- There, the pitch material is contacted with a solvent selective for aliphatic hydrocarbons introduced by way of line 3. Extraction may be accomplished using a variety of conventional techniques and apparatus on either a batch or continuous basis. Generally it is preferred to maintain an excess of solvent within the extraction zone; a weight ratio of solvent to pitch ranging from about 2:1 to 3:1 givingsatisfactory results. Extraction temperatures preferably range from room temperature to about the boiling point of the solvent or from about 20 to about C.

However, even higher temperatures may be used. Contact time ranges from a few minutes to about 2 hours depending upon temperature and solvent to pitch ratios.

In the extraction zone, aliphatic hydrocarbon components of the pitch are leached from the pitch particles and are dissolved in the solvent. A solvent fraction, rich in dissolved aliphatics, is separated from the pitch particles by settling or filtration, and is passed via line 4 to distillation zone '5. A bottoms fraction 6 comprising extracted aliphatic hydrocarbons is recovered as a product of the process while the overhead stream comprising solvent is routed back to extraction zone 2.

Leached pitch particles are passed by means 7 to washing zone 8. There, the pitch is washed with a small quantity of solvent which may be recovered by distillation. Pitch particles now substantially depleted in aliphatic hydrocarbon content, are then subjected to a high temperature processing step which may comprise either thermal-cracking or delayed coking. If thermal cracking is utilized, then pitch is passed from washing zone 8 to thermal cracking zone 11 by way of conduit means 9 and 10. Thermal cracking may be carried out in conventional fashion at temperatures generally in the range of 700 to 900C to yield an oil fraction 12, a coke residue 13 and of course a gas stream (not shown).

If delayed coking techniques are utilized, then the pitch is passed to delayed coking zone 15 by way of conduit means 9 and 14. Like in thermal cracking, products of the delayed coking step comprise a coke residue 16 and an oil fraction 17. The delayed coking step is carried out in conventional fashion in the same manner used in the delayed coking of petroleum residuals. Oil obtained from either thermal treatment is then passed to distillation zone 18 where it is separated into an overhead distillate stream 19 and a residual pitch binder fraction 20. Distillate stream 19 finds use as a raw material for the separation or synthesis of a variety of aromatic compounds while the pitch fraction constitutes a high quality binder for electrodes, pitch fiber pipe and roofing materials.

Properties and composition of low temperature lignite pitch used as the starting material in our process will vary somewhat depending upon the properties of the lignite and the conditions used in the low temperature carbonization step. A typical analysis of the material is as follows:

TABLE 1 In addition, extractable aliphatic content of the low temperature pitch ranges from about 5 to about 20 percent and commonly is onthe order of 8-10 percent. Bituminous. pitch, on the other hand, contains only traces of aliphatics.

TABLE 3 Electrode Strength (Kg/cm Electrode Resistivity (ohm-cm) Binder Aliphatics Aliphatics Aliphatics Aliphatics (7:) Present Removed Present Removed Solvents suitable for use in the extraction step genera ally comprise saturated, paraffinic hydrocarbons of intermediate boiling range. Preferred solvents include paraffmic hydrocarbons having 7 to 9 carbon atoms. It was found that n-heptane was suitable for use but that n-hexane and n-pentane were less satisfactory in that contained in the crude pitch. Aliphatics extracted generally have a boiling point in excess of about 300C and find use in the production of biodegradable synthetic detergents.

The following example illustrates a specific embodiment of our process.

EXAMPLE A crude lignite pitch, having properties as set out in Table l, was obtained by low temperature carbonization of lignite coal. It was processed in accordance with the flowsheet set out in the FIGURE using trimethylpentane as a solvent in the extraction step. After thermal cracking and distillation, the binder pitch product obtained had the following characteristics:

TABLE 2 Carbon 89.9 Hydrogen (%1) 5.03 Carbon/hydrogen atomic ratio 1.49

Softening point ("C 113 A second binder pitch was prepared in a similar fashion except that the aliphatic extraction step was omitted. The two pitches were then evaluated for use as a binder material for making carbon electrodes for metallurgical use. Results of these comparative testsare as follows:

As may be seen from Table 3, removal of aliphatics from the crude pitch results in improved properties of the binder pitch. Electrodes prepared using a binder pitch from which aliphatics had been removed showed generally lower electrical resistivity and substantially higher physical strength than did electrodes prepared from aliphatic-containing pitch.

What is claimed is:

1. A process for producing a composition suitable for use as a binder. for carbon particles which comprises:

treating a crude pitch, obtained as the distillation residue of tar produced by the low temperature carbonization of lignite coal and further characterized by containing from about 5 to 20 percent extractable aliphatic hydrocarbons, by solvent extraction, using as a solvent a liquid consisting essentially of a saturated aliphatic hydrocarbon having 7 to 9 carbon atoms, to remove a substantial portion of aliphatic hydrocarbons contained in said crude pitch fraction;

thermally cracking the residue from said solvent extraction step at temperatures within the range of 700 to 900C to produce an oil fraction a gas fraction and a coke fraction, and

distilling said oil fraction to recover an overhead distillate stream comprising aromatic compounds and a residual binder pitch product.

2. The process of claim 1 wherein more than percent of the aliphatic hydrocarbons contained in said crude pitch are removed in the solvent extraction step.

into an electrode. 

2. The process of claim 1 wherein more than 75 percent of the aliphatic hydrocarbons contained in said crude pitch are removed in the solvent extraction step.
 3. The process of claim 2 wherein rich solvent from the extraction step is distilled to recover an aliphatic hydrocarbon product stream and a recycle solvent stream.
 4. The process of claim 3 wherein the solvent is a branched chain aliphatic hydrocarbon having 8 carbon atoms.
 5. The process of claim 4 wherein the solvent is trimethylpentane.
 6. The process of claim 3 wherein said pitch binder product is mixed with particulate coke and is formed into an electrode. 